Handling infidelity when you catch your girlfriend with someone else is rough, but the best thing is to simply keep quiet about the whole episode.
Refrain from screaming and abusing.
Break up with her and take control of your life or allow her to continue doing what she has been doing for a while, only if you think you can make her realise.
Try to speak to her and learn her true feelings. Is she is actually in love with someone else or they are just friends? You can give it another try in case you think you can forget and forgive.
If you say you will forgive, you have to mean it and be sure that your partner is ready too. Otherwise, your relationship may turn into a vicious cycle of mistrust, revenge and unspoken hate.
Try to understand what made your girlfriend cheat on you. Analyse if there was something wrong in your behaviour and the relationship between both of you, which led such a situation.
Refrain from spreading rumours and personal information about your ex-girlfriend , once you decide to part ways. It’s always a good idea to part on a pleasant note. Try not be bitter about your relationship and do not be mean.